Tutors will be expected to abide by minimum qualification standards and sign up to a code of ethics following concerns that poor teaching may be damaging pupils’ education.

It is feared that some tutors may be preying on parental anxiety over school places and exam grades by “over-tutoring” children, with reports of some infants aged just three being given booster sessions.

Experts said there was also a problem of tutors undermining the work being done in school and a lack of quality control.

It comes after a leading headmaster criticised private tutoring for “devouring” children’s free time as parents subject them to extra classes after school and at the weekend.

Ben Thomas, head of Thomas’s Battersea, said he had heard of tutoring agencies that were “starting to work on three-year-olds” for the school’s entrance exams.

One study last year suggested more than half of parents who put sons and daughters through school admissions tests pay for an academic coach or private tutoring company, while thousands more invest in revision books or past papers to give children the edge.

Now the Centre for Market Reform of Education, a think-tank, is planning to establish the first national association for tutors – with backing from a number of major tutoring companies – to develop industry standards and improve the consistency of teaching.

A consultation on the new Tutoring Association was launched on Wednesday that will require tutors to sign up to a new code of ethics, take part in vetting procedures and meet minimum qualification thresholds.

It says that tutors should hold university degrees in their chosen specialist subject when teaching children aged 11 upwards and general degrees in any subject for those tutoring primary-age pupils.

Although membership will not be compulsory, it is intended to act as a “kite-mark” for the industry.

James Croft, the think-tank’s director, said there was “precious little guidance for parents seeking tutors, who are often ill-equipped to assess their children's precise needs”.

He added: “There’s the occasional problem of tutors undermining the work being done in school by teaching different methods, but more problematic is just this widespread lack of clarity about what tutors are supposed to be achieving and how to gauge whether they are helping.

“On the other side of the equation, there’s the problem of over-tutoring in preparation for exams, which can obviously be counter-productive.

“Underlying all this is the problem that there’s little assessment of pupil’s needs going on that is separate from the tutoring process.

“Presented with an anxious parent who is insistent that their child needs help, a freelance [tutor] is unlikely to turn that customer away.”

Mr Croft said the lack of proper qualifications among tutors was a major problem with no rules preventing people setting themselves up as freelance tutors irrespective of their expertise.

Research has also shown that a number of legitimate tutoring agencies “appear not to require degree-level subject knowledge or teaching qualifications” among their staff. A previous study found 57 per cent demanded a relevant degree and 78 per cent wanted teaching experience, while 90 per cent of tutors were hired by parents “through word of mouth or other means”.